Two-filament light bulbs designed for three-way sockets provide the conventional "spot" center contact at the base of the bulb for one filament and another contact for the second filament, presently a "ring" centered on the "spot" center contact. Conventional three-way sockets provide the proper switching sequence to the spot and ring contactors of the two-filament bulbs to provide the option of any of three light intensities, one filament alone (low intensity), the other filament alone (higher intensity), or both filaments concurrently (maximum intensity).
Often the option of three intensities (low, medium, high) is of no advantage, but four turns of the three-way socket switch required each time the bulb is lighted and turned off, is inconvenient and a nuisance when only a single intensity is desired. In such cases, it is common for a user to replace the three-way bulb with a predominently desired intensity single-filament bulb, connected through the centered spot contact on its base, but four turns of the switch handle are still required from "off" to "off" (off-off-on-on-off).
Two-filament bulbs designed for three-way sockets provide the conventional "spot" center contact at the base of the bulb for the aforenoted one high-intensity filament and another contact for the aforenoted low-intensity filament, presently a "ring" centered on the "spot" center contact. Conventional three-way sockets provide the proper switching sequence to the spot and ring contactors of the two-filament bulb's aforenoted low intensity filament, the high intensity filament, or both filaments concurrently for (maximum intensity).
Note that three-way socket switches connect power to the radially outward socket contact (the ring contactor) and next to the center socket contactor (the spot) and finally to both socket contactors. Applicant has recognized that, with the existing switching sequence described above, for any filaments connected to the ring contactor (radially outward contactor of conventional three-way sockets) the desired "off"-"on"-"off"-"on" lighting switching sequence is achieved.
In other words, if in a conventional three-way socket, the "spot" contactor can be isolated and a single-filament bulb or one or both of the filaments of the three-way bulb can be connected to the radially outward "stub" contactor exclusively, the light switching sequence will be "off"-"on"-"off"-"on".